1. Field of the Invention
The present invention relates to a system control method that enables managing of optical network units (ONUs), securing of communication bands, and identifying of communication data in each of plural systems that are disposed to share an optical fiber when plural optical access devices are installed.
2. Description of the Related Art
Due to the increased demands for broad bands, phone line-based access technologies such as Digital Subscriber Line (DSL) and the like are replaced by large-capacity access lines using optical fibers as user-dedicated access lines. Optical access line type is generally classified into two types. One type is called “media converter (MC)” and this is a method of connecting optical fibers from a station of a communication service provider to a user's home or building to establish optical fibers in a one-to-one (point-to-point) topology. The other type of method is called PON (Passive Optical Network), and this provides an optical coupler (optical splitter) in an optical fiber interval that is disposed in an interval from a station to a user to split an optical signal from a station into 32, 64, or 128 optical fibers. Currently, the PON system, which provides point-to-multipoint topology, has drawn attention for optical access services. One reason is that an optical fiber from the station to the splitter is shared by all the users in the PON system and therefore costs for establishing lines and maintenance-related costs may be reduced. The other reason is that the PON system requires a signal multiplexing transmission structure because of signals from plural users are arranged and received on the station side. Multiplexing methods currently adopted include TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access) and so on. Utilizing these functions provides the PON system with an advantage that mounting optical devices may be done at low costs with respect to devices on the station side.
Currently, there are discussed recommendations (ITU-T Recommendation G. 984.1, “Gigabit-capable Passive Optical Networks (G-PON): General characteristics”, TTU-T Recommendation G. 984.2, “Gigabit-capable Passive Optical Networks (G-PON): Physical Media Dependent (PMD) layer” specification) of G-PON (Gigabit-capable PON) for ITU-T (International Telecommunication Union Telecommunication Standardization Sector). The recommendations have been completed for the main parts, and vendors started to release G-PON products on the market. At the same time, carriers from each country started optical access services that employ G-PON. Also, some carriers are providing optical access services whose infrastructure is based on GE-PON (Gigabit Ethernet PON) standardized in IEEE (Institute of Electrical and Electric Engineers).
While introduction of optical access systems is accelerated, next-generation optical access systems are already under discussion in FSAN (Full Service Access Network) and IEEE (IEEE 802.3av) that are standardization groups regarding optical access technologies. In terms of transmission path multiplexing methods, IEEE 802.3av moves toward speed-up of TDMA and FSAN considers WDMA as another candidate and therefore both do not reach one conclusion at the current stage. However, both adopt 10 Gbps as a reference respective of downstream transmission speed.
Upon high bit rate (broad band) transmission of 10 Gbps, problems with wavelength distortion occur due to S/N deterioration and/or wavelength dispersion. Accordingly, improving the control of output of a laser or wavelength for suppressing wavelength dispersion is considered as an important technology. Further, the cost of addressing the problems should be in consideration of the market cost not in terms of high-cost devices that is used for a repeating system.
What carriers' value most is not depending on the next-generation PON methods but the ability to coexist with existing B-PON (Broadband PON, which is standardized in ITU-T in Recommendation G.983.x series)/GE-PON/G-PON. In the FSAN, it is currently researched to make the existing PON coexist with next-generation optical access system (NGA) through WDM, and therefore, research is undergoing in terms of costs and performance of wavelength filters to be introduced on the ONU (Optical Network Unit; one of the PON equipments located in the user sites) side. It is necessary to perform technological reviews on technologies in order to realize 10 Gbps having wavelengths applicable to the NGA restriction. The NGA review group of the FSAN is considering adopting a wavelength dispersion compensation function for electrical signals as well as light, a semiconductor optical amp. (such as SOA, EDFA (Erbium Doped Fiber Amplifier), PDFA (Praseodymium Doped Fiber Amplifier)), an external modulator (Electro-Absorption Modulator Integrated Distributed Feedback Laser; EA-DFB), high-sensitive receiver (Avalanche Photo Diode; APD), and an FEC (Forward Error Correction) to realize 10 Gbps transmission in existing optical fibers (split number of 32 or 64, transmission distance of 20 km).
Therefore, multi-system coexistence is also under discussion which is carried out by time multiplexing using the same wavelength in optical characteristics for a case where plural PON systems coexist. Such a system construction is expected to be necessary in the future from the point of view of costs, which are considered the most important in optical access.